1. Field of the Invention
The invention resides in the field of nebulizers for producing fine liquid droplets or aerosols.
2. Description of the Prior Art
A variety of types of nebulizers exist in the prior art. There are, for example, concentric nebulizers in which a flowing stream of liquid is concentrically introduced into the center of a surrounding high velocity stream of gas. When the liquid and gas are brought into contact at the tip of the nebulizer, the emerging gas shears and vibrates the liquid through turbulence breaking it into fine droplets. There are some drawbacks to this design, specifically because of the need for small dimensions and close tolerances, a tendency of the apparatus to clog from the small particles which may be contained in the sample. Dimensional changes with changes in temperature may also be a problem which is normally solved by using glass for construction. Glass as a material is obviously very delicate and cannot be used with hydrafluoric acid.
Cross-flow nebulizers work on the same principle of turbulence and shearing except that the liquid stream and gas stream interact at a right angle rather than concentrically. This approach is equally subject to the problem of clogging when small diameter liquid tubes are used. Additionally, the alignment of the gas and liquid orifices is critical and may drift due to thermal expansion and material creep.
A somewhat different form of cross-flow nebulizer uses a slot or sluiceway instead of a tube for conveying the liquid to the gas. Clogging is less likely to occur but liquid flow cannot be well controlled. Thus where precision is required, in analytical instruments for example, this form of nebulizer is not well suited.
An entirely different approach is to be found in the design of ultrasonic nebulizers. In these, the liquid is brought into contact with a vibrating crystal whereupon the vibrational energy is transferred to the liquid and results in the desired break-up. These types are used primarily in analytical applications, and while more efficient than the above described pneumatic devices, they are subject to a lack of repeatability in cases where the liquid contains salts or organic material which leave a coating on the transducer. In addition, again in comparison to the pneumatic types, they are large, expensive, and awkward to handle.
In contrast, the invention disclosed herein is a unique departure in concept from the devices described above.